In Patent Document 1, the applicant has previously provided a flat, hollow brushless servo motor for performing a cutting process, wherein a cutting tool is mounted on both ends of a motor shaft and a workpiece is pressed from both sides.    [Patent Document 1] WO 2005/013463 Pamphlet
With a workpiece cutting tool that uses a brushless motor of this configuration, a cutting process is performed by the cutting tool while cutting processing oil is supplied to the workpiece in a position adjacent to the motor. Therefore, the cutting processing oil readily enters the motor from a shaft end part of the motor shaft. The cutting processing oil contains a large quantity of metal cutting powder produced by the cutting process. When metal cutting powder mixes in with the cutting processing oil and enters the motor, motor coil ground faults, insulation problems, and other adverse events readily occur more quickly than during use under normal usage circumstances. In view of this, an oil seal or another flexible contact seal is installed between the motor shaft and the motor housing in order to prevent the metal powder and other impurities undesirably combining with the cutting processing oil.
However, in this case, the metal cutting powder comes into direct contact with the contact portion between the contact seal and the outer periphery surface portion of the motor shaft. As a result, the portion (lip) in the contact seal in contact with the motor shaft is quickly abraded and damaged by contact with the metal cutting powder, and its longevity is extremely shortened.